1. Field of the Invention
The present invention relates to a positive type anionic electrodeposition photoresist composition having excellent running stability during electrodeposition and good coatability, which is suitable for use as a resist enabling formation of highly reliable conductor image, particularly as an etching resist for production of printed wiring board, as well as to a process for pattern formation using said resist composition.
2. Description of the Prior Art
The printed wiring boards used in electronic apparatuses, etc. are produced mainly by (a) a pattern printing process which comprises conducting screen printing on an insulating substrate having a conductor layer on the surface and (b) a substractive process which uses a circuit pattern formed by photolithography using a photosensitive dry film. With the recent technical advancement to a higher density and a higher accuracy, however, the printed wiring boards are required to have a finer circuit pattern and a smaller through-hole diameter. To meet such requirements, there were proposed various processes for production of printed wiring board using a positive type electrodeposition photoresist.
As compositions capable of forming a positive type electrodeposition photoresist, there were proposed water-soluble or water-dispersible compositions such as a composition using, as a main component, a resin obtained by bonding a quinone diazide sulfonic acid to a base resin (e.g. an acrylic resin having an ion-forming group) via a sulfonic acid ester bond (U.S. Pat. No. 4,673,458); a composition using, as a main component, a resin obtained by bonding hydroxylamine and quinone diazide sulfonic acid to a base resin (e.g. an acrylic resin having an ion-forming group) via a urethane bond and a sulfonimide bond (U.S. Pat. No. 4,975,351); a composition using, as a main component, a photosensitizer mixture obtained by reacting an acrylic resin obtained by copolymerizing a polymerizable monomer having a relatively long side chain having, at the end, an acid group (e.g. a carboxy group), with an epoxy compound, a phenolic hydroxyl group-containing aromatic or heterocyclic carboxylic acid and quinone diazide sulfonic acid halide (U.S. Pat. Nos. 5,055,374 and 5,166,036); a composition obtained by mixing a base resin (e.g. an acrylic resin having an ion-forming group) with a compound or resin obtained by bonding hydroxylamine and quinone diazide sulfonic acid to a compound or resin having a hydroxyl group, via a urethane bond and a sulfonimide bond (U.S. Pat. No. 5,134,054); a composition using, as a main component, a photosensitive resin having a phenolic hydroxyl group and a carboxyl group or an amino group in the polymer molecule, in which resin a quinone diazide sulfonic acid is introduced via a sulfonic acid ester bond (U.S. Pat. No. 4,673,458); a composition obtained by mixing a carboxyl group-containing polymer with a phenolic hydroxyl group-containing polymer in which quinone diazide sulfonic acid is introduced via a sulfonic acid ester bond [U.S. Pat. No. 5,080,998 and Japanese Patent Application Kokai (Laid-Open) No. 100073/1991]; a composition using, as a main component, a mixture of a carboxyl group-containing acrylic acid and a sulfonic acid ester between a phenolic hydroxyl group-containing aromatic carboxylic acid ester and quinone diazide [Japanese Patent Application Kokai (Laid-Open) No. 100074/1991]; and a positive type electro-deposition resist composition comprising a block. copolymer composed of a carboxyl group-free polymer segment and a carboxyl group-containing polymer segment, an alkali-soluble polyphenol and a positive type photosensitizer, and a resist composition obtained by, in the above resist composition, bonding the photosensitizer to other component [Japanese Patent Application Kokai (Laid-Open) No. 281671/1991].
The above conventional compositions, however, have the following problems, and solutions thereto are needed.
That is, in the resin systems in which a photo-sensitive group is introduced via a sulfonic acid ester group, it is necessary to subject the hydroxyl group (e.g. a phenolic hydroxyl group) of a resin and a sulfonic acid halide to dehydrohalogenation to form a sulfonic acid ester and thereby introduce a quinone diazide group. This reaction is a polymer reaction, wherein it is difficult to introduce a photosensitive group quantitatively. In the reaction, it is also difficult to remove, after the reaction, a halogenic acid salt (a by-product) and purify the product; the production time is long; thus, the reaction is not favorable for industrial use.
To avoid the formation of by-product in the above polymer reaction, there is a system using a resin obtained by reaction a naphthoquinone diazide sulfonic acid halide with hydroxylamine via a sulfonamide bond, reacting the reaction product with a diisocyanate (e.g. toluene diisocyanate), and reacting the resulting intermediate having a photosensitive group and an residual isocyanate group, with a hydroxyl group-containing resin. This system is favorable in that the yield in polymer reaction is high and that no purification step is required, but has problems in that the steps up to production of intermediate are complicated and require a long time.
In the above systems using a resin in which a photosensitive group is introduced, the photosensitive group is located randomly in the resin; therefore, when the system is made into an aqueous dispersion, the resin portion containing a photosensitive group of high hydrophobicity is easily present on the surface of dispersed particles. As a result, the aqueous dispersion has low stability and tends to generate a deposit; the azide group contacts easily with a basic substance (e.g. an amine) present in the aqueous layer in a large amount and is decomposed, resulting in reduced photosensitivity. Thus, the systems have a big drawback as an electrodeposition resist which must have long-term stability when made into an aqueous dispersion.
Meanwhile, in the systems using a resin in which a photosensitive group is introduced via a sulfonic acid ester group, the sulfonic acid ester group is hydrolyzed easily; therefore, the systems, when used as an electrodeposition resist solution, have even lower stability during storage and during running. In the system using a resin in which a photosensitive group is introduced via a sulfonic acid imide bond and a urethane bond, the problem associated with hydrolysis is significantly improved, but the exposed resist portion is slow in dissolution in developer and the development must be conducted at high temperatures.
In order to solve the above problems, there was proposed an electrodeposition resist which is an aqueous dispersion of a composition comprising a water-soluble or water-dispersible resin and a quinone diazide type photosensitizer. There were proposed, for example, (1) a composition comprising an alkali-soluble resin (e.g. a phenolic resin) (this alkali-soluble resin is in use in LSI production) and a naphthoquinone diazide sulfonic acid ester of a polyhydroxybenzophenone, and (2) a composition obtained by using, in the above composition (1), a water-soluble or water-dispersible resin (e.g. an acrylic resin) in place of the phenolic resin (his phenolic resin is not preferable for use in an electrodeposition resist for production of printed circuit board, in view of the water-dispersibility and the properties of the film formed therewith). With these compositions, however, their aqueous dispersions have no sufficient stability and generate a deposit easily; in the aqueous dispersions, since part of the photosensitizer is present on the surface of dispersed particles, the azide group of the photosensitizer contacts with a basic substance, resulting in its decomposition and consequent reduction in photosensitivity. Further, when a photosensitizer of sulfonic acid ester type is used, the sulfonic acid ester is hydrolyzed, resulting in reduction in stability of aqueous dispersion; thus, it is difficult to obtain an electrodeposition resist solution having excellent running stability over a long term.
In order to improve the stability of an aqueous dispersion, it was proposed to use a comb-structured acrylic resin obtained by copolymerization of a particular monomer of relatively long chain polyester or polyether type having an acid group at one end and a polymerizable unsaturated group at the other end (in said resin, the ion-forming group is distant from the resin skeleton which is hydrophobic) and thereby allow a highly hydrophobic quinone diazide type photosensitizer to be easily present inside the resin particles dispersed in water.
By this approach, there can be obtained an aqueous dispersion having a considerably improved storage stability, but its running stability over a long term is not sufficient. Further, in order to obtain said acrylic resin, a special monomer must be be used and the process for production thereof is complicated and requires a long time.
Furthermore, said monomer has a relatively large molecular weight and has a low copolymerizability with ordinary acrylic ester type monomers, etc., and tends to remain unreacted in produced resin or form a homopolymer. The unreacted monomer and homopolymer tend to act as water-soluble components when being in an aqueous dispersion and enables the formation of an aqueous dispersion of relatively good storage stability. The aqueous dispersion, however, is not sufficient as an electrodeposition resist because, when it is used in electrodeposition and there is conducted circulation of electrodeposition solution by pump (this is requisite in electrodeposition), the dispersed resin particles tend to cause fusion with each other and generate an agglomerate in the solution, which easily causes (1) deposition of said agglomerate on formed resist film and (2) plugging of filter used in circulation system.
Also in an electrodeposition resist which is an aqueous dispersion of a mixture comprising a carboxyl group-containing polymer and a photosensitizer obtained by introducing a quinone diazide type photosensitive group to a phenolic hydroxyl group-containing polymer (e.g. a polyvinylphenol) via a sulfonic acid ester bond, the running stability is insufficient and the photosensitizer used therein, which is a product of polymer reaction, has problems as mentioned previously.
With a composition which uses, as an acrylic resin, a block copolymer composed of an ion-forming group-containing segment-and an ion-forming group-free segment and further comprises an alkali-soluble phenolic resin and a photosensitizer, there can be formed a resist pattern of good resolution; however, in order to obtain such an acrylic resin, an expensive polymerization initiator must be used and the production process is complicated, both of which are very disadvantageous economically.
Moreover, the resist film obtained by conducting electrocoating using any of these compositions has various drawbacks. That is, the resist film is low in contrast (difference in solubility in developer between exposed portion and unexposed portion); can be subjected to development only under limited development conditions (temperature and time); and has no sufficient etchant resistance and, when the copper or circuit substrate to be etched has a large thickness, must be etched under severe etching conditions (long time and/or high temperature), resulting in easy attack of resist film and consequent easy appearance of defect in circuit pattern or through-holes.
Hence, the present inventors made an extensive study in order to develop a positive type electrodeposition photoresist composition which can be produced without using any complicated and long reaction or any complicated process, which can be made into an electrodeposition resist solution of excellent storage stability and circulation stability and can give an electrodeposition solution of high running stability even at a low-turnover speed, and which can form a resist film of high contrast and excellent etchant resistance, as well as a process for formation of highly reliable pattern using said composition. As a result, it was found that a composition, which can solve all the problems mentioned above, can be obtained by mixing a particular water-soluble or water-dispersible acrylic resin, a resin having a hydroxystyrene unit and an ester between quinone diazide sulfonic acid and a polyhydroxybenzophenone to prepare a composition, neutralizing part or all of the carboxyl groups of the composition with a basic substance and dispersing the neutralization product in water, and further that, by using said composition, a highly reliable pattern can be formed. The finding has let to the completion of the present invention.